1. Field of the Invention
This invention pertains in general to MEMS device, and more specifically to an improved cantilever design for usage in a MEMS device
2. Description of the Related Art
Traditionally, many MEMS devices are actuated by simple, single-stage cantilevers, which are composed of a cantilever plate, a moveable contact and a stationary contact. When a typical metal-metal contact MEMS switch is turned on, the cantilever plate is actuated until the moveable contact and the stationary contact achieve closure, and this closure is typically achieved in a single stage of movement of the cantilever plate (e.g., a hinge on the device allows the plate to be lowered in one movement). When the device is turned off, the moveable and stationary contact interface is broken as these two contacts are separated, and the device reassumes the open state. MEMS switch devices are important for use in various types of applications. For example, they can be used in mobile phones for switching RF signals between transmit and receive modes and other related functions, micro-relays that can be used in automated test equipment (ATE), phased radar array, and other applications. MEMS switch configurations include but are not limited to SPST, SPDT, SP4T, DPDT, SP7T and SP8T. MEMS switches can be used for DC and RF applications.
For long-term reliability of switches such as contact switches and other MEMS cantilever devices, this “simple” cantilever structure does not adequately provide the actuation forces necessary to overcome stiction/adhesion forces, such as those caused by welding, electrical charging and device contamination. For many MEMS applications, especially those requiring a high quality interface between the contact surfaces, such as MEMS switches, this may be detrimental to reliability and device lifetime. Without a sufficiently strong force, the two contacts may never achieve full closure. Further, the single-stage cantilever design commonly only allows for a small gap between contacts before closure, thus resulting in inferior isolation.
In addition, the lifetime of a MEMS switch device can be greatly decreased due to the manner in which the two contacts are brought together and then pulled apart. If the first contact is brought down too rapidly and if it does not contact the other contact in a sufficiently gentle manner, this can result in damage to the device that over a period of time can reduce the overall life of the device. Similarly, if the contacts are pulled straight apart from each other and in a manner that is not sufficiently gentle, this can again cause unwanted damage to the contacts, decreasing the life of the device.
Another issue in single-stage cantilevers is the increase in resistance due to contaminant build-up and other particulates interfering with contact closure. Many single-stage cantilevers do not have any mechanism for removing this type of build-up on the contact surface. Single-stage cantilevers commonly also have low actuating forces, and so they may not have the adequate measures for removing the contamination or otherwise providing a mechanism for removal. Thus, again, these types of single-stage cantilever devices may suffer from shortened lifetimes.
Therefore, there is a need in the art to for a MEMS device with cantilever actuator that provides more long-term reliability, provides the higher actuation forces necessary to overcome stiction or adhesion forces, provides a sufficiently large gap for improved isolation, provides better interface quality that includes fewer contaminants, and provides a mechanism for more gentle, easier contact closure and separation.